Along with recent developments in information-technology related equipment, there has been demand for laser scanners and copiers for printing letters and images faster and more densely. For such speeding up and densification, a high-speed and stable rotation of polygon mirror for scanning a laser is necessary. In the most current laser scanner bearings, from the perspectives of rigidity and stability with respect to a high-speed whirl (HFW), an aerodynamic pressure bearing mechanism with herring bone (hereinafter accordingly abbreviated as “HB”) grooves is used.